11:59PMAM (TYPO!!!):
Miss Loi waits patiently in the car, with sunglasses on.
12:00PM:
Target appears – spotted walking towards another car. Miss Loi’s eyes brightens. *Grips steering wheel*
12:02PM:
Aunty (i.e. The Target) takes an age to squeeze her groceries into car. Miss Loi getting impatient.
12:03PM:
Aunty completes squeezing of groceries into car. Aunty drives out of parking lot. Miss Loi takes off sunglasses and quickly zooms into vacated lot before the Ah Beng car behind beats her to it.
12:04PM:
After a thorough scan across the horizon, Miss Loi tears her parking coupon (like all good parking citizen should do), as shown below:
– “scheduled” to start at 12:20PM
12:05:00PM:
Miss Loi hippity-hippity hops away from her car.
1:20PM:
Miss Loi hippity-hippity hops back to find this on her car:
(click to enlarge)
1:30PM:
A distraught Miss Loi calls Mr Loi:
Bro! You wouldn’t believe how SUAY I was at the carpark just now! I tore my coupon to start at 12:20PM, left my car at 12:05PM, and I got summoned at 12:08PM! They employ ninjas as parking attendants these days is it?!!!!
Mr Loi replied in a calm voice:
Sigh … that is a ‘hot’ carpark with a parking attendant coming every hour. Please brush up your rusty A-Level Probability & Statistics and solve the following question to know your chances of getting caught, and try to lower your probability of getting caught the next time:
Assuming that the parking attendant visits the carpark once every hour, and that the probability of her turning up to check at any given minute is 1/60.
Miss Loi tears her coupon to commence at 12:20PM and left her car at 12:05:00PM.
- Find the probability of the parking attendant first appearing at 12:08PM.
- Find the probability of Miss Loi getting caught i.e. the parking attendant appearing at anytime between 12:05-12:19PM.
- What is the latest commencing time she should tear in her coupon in order to have at most a 10% chance of getting caught by the parking attendant?
* Take each minute as a discrete random variable
1:35PM:
An angry Miss Loi hangs up the phone abruptly 🙁
